docs: def fmt_sia(sia, ces=True):
      """Format a |SystemIrreducibilityAnalysis|."""
      if ces:
          body = (
              '{ces}'
              '{partitioned_ces}'.format(
                  ces=fmt_ces(
                      sia.ces,
                      'Cause-effect structure'),
                  partitioned_ces=fmt_ces(
                      sia.partitioned_ces,
                      'Partitioned cause-effect structure')))
          center_header = True
      else:
          body = ''
          center_header = False
  
      title = 'System irreducibility analysis: {BIG_PHI} = {phi}'.format(
          BIG_PHI=BIG_PHI, phi=fmt_number(sia.phi))
  
      body = header(str(sia.subsystem), body, center=center_header)
      body = header(str(sia.cut), body, center=center_header)
      return box(header(title, body, center=center_header))